Standard assemblies for implements such as chisel plows and field cultivators typically include a spring trip shank assembly extending downwardly to a tool-receiving end which mounts a shovel, point or sweep. Previously available mounting structure included bolts extending through holes in the tool and the shank to secure the tool. When the tool in such an assembly has to be replaced because of wear or damage, the bolts must be removed. Wear and corrosion of the bolts substantially hinders removal and often makes the replacement a difficult and time-consuming task.
Several solutions to the problem of easily and quickly replacing worn elements such as sweeps on shanks have been developed over the years, including adapter brackets providing a self-locking fit with a matching taper on knock-on sweeps, and frangible pins. Most retaining devices have suffered from one or more problems, including need for additional parts and the loss of sweeps when encountering high removal forces during transport and during rebounding of the shank from a tripped position. To reduce incidences of sweeps falling off the shanks in quick mount arrangements, some manufacturers have offered detent mechanisms such as a retaining clip in the form of a sheet metal stamping with a spherical protrusion that fits into a hole in the sweep. To release the sweep, a screwdriver or other tool is used to depress the clip and move the protrusion away from the hole. Other detent arrangements are shown, for example, in U.S. Pat. Nos. 3,061,021 and 6,289,996. Such detents generally help retain the sweeps on the shanks, but the forces exerted on a sweep, particularly forces exerted on deep tillage tools, can be so great that the sweep fails to stay on the shank. The geometry of most previously available sweep detent arrangements, including non-symmetrical mating surfaces on some, usually limits penetration of the retaining surface into the hole so that retaining forces are limited. Some care must be taken to align the protrusion with the hole, and part tolerances, variations in force used to mount the sweep, or lack of indexing of the clip relative to the shank can make such alignment troublesome. A relatively small, ramped contact area between the clip and the hole also increases the potential for losing a sweep. Soil moving up and around the stem portion of the sweep can move the clip from the detent position or wear away the clip until it is ineffective for holding the sweep on the shank. Extreme forces on the detent, such as those which occur during rebound, can also cause deformation of the detent. If the detent deforms, loosened sweeps can unacceptably dangle from the shank or be lost. A hefty detent construction or frequent detent replacements are therefore usually required.
In copending and commonly assigned U.S. application entitled KNOCK-ON SWEEP STRUCTURE AND TOOLS THEREFOR, Ser. No. 09/982,901, filed 19 Oct. 2001, a sweep assembly is described having a retainer fabricated from wire spring material and supported in a groove on the underside of the wedge support which mates with stem portion of the sweep. The end of the wire is biased toward a contact area on the top edge of a slot in the stem to prevent the sweep from slipping down away from the wedged mounted position. To remove the sweep, a tool is inserted through the slot to depress the retainer end, and the sweep is forced downwardly off the wedge support. A common problem with sweep detents is most have a fixed detent position, and manufacturing tolerances in the sweep and support can result in an overly loose or tight fit at the detent position. If there is excess looseness in the fit between the sweep and sweep adapter, the detent structure may have to bear substantially all the retaining load. If the fit is too tight, the sweep may never reach the detent position and may be lost during transport or at the end of a shank rebound. Providing the manufacturing tolerances necessary for proper alignment can make the cost of the device prohibitive. Often the operator must apply a very large driving force to the sweep with a hammer or other tool to provide the wedge lock or assure that the sweep reaches the detent position.